Power transmission apparatus, method for controlling power transmission apparatus, and recording medium

ABSTRACT

A power transmission apparatus wirelessly communicates with a power reception apparatus using an antenna, wirelessly transmits power to the power reception apparatus using the antenna, measures, in a period during which the transmission of the power is stopped, one or both of a voltage and a current output from the antenna, performs, based on a measurement result obtained by the measurement, a determination process for determining that an object different from the power reception apparatus is present, restricts, in a case where it is determined that an object different from the power reception apparatus is present as a result of the determination process performed by the first determination unit, the transmission of the power, and controls the first determination unit not to use in the determination process the measurement result obtained by the measurement in a period during which communication is performed.

BACKGROUND Field

The present disclosure relates to a power transmission apparatus, amethod for controlling a power transmission apparatus, and a recordingmedium.

Description of the Related Art

In recent years, a technique for a wireless power transmission systemhas been widely developed. Japanese Patent Application Laid-Open No.2017-70074 discusses a power transmission apparatus and a powerreception apparatus compliant with a standard formulated by a wirelesscharging standards body called the Wireless Power Consortium (WPC)(hereinafter referred to as the “WPC standard”). Communication betweenthe power transmission apparatus and the power reception apparatus isachieved by superimposing a signal on power to be transmitted, using anantenna for use in wireless power transmission.

Japanese Patent Application Laid-Open No. 2017-70074 discusses a methodfor, in a case where an object (hereinafter referred to as a “foreignsubstance”) different from a power reception apparatus is present in therange where a power transmission apparatus can transmit power,specifying the presence of the foreign substance, and based on theresult of the specifying, restricting the transmission of power.

Japanese Unexamined Patent Application Publication No. 2018-512036discusses a method for, based on the amount of attenuation in thevoltage value of a power transmitter in the period during which thevoltage of the power transmitter gradually decreases after thetransmission of power is stopped, determining whether an object ispresent near the power transmitter.

SUMMARY

In a case where an antenna for use in wireless power transmission isused in communication between a power transmission apparatus and a powerreception apparatus, the following issue arises in a method discussed inJapanese Unexamined Patent Application Publication No. 2018-512036. Thatis, if communication using an antenna for use in wireless powertransmission is performed when a voltage is measured in the periodduring which the transmission of power is stopped, a change in theamplitude of a signal for the communication is reflected on the power,i.e., the voltage to be measured. Thus, the voltage to be measured isinfluenced not only by an object but also by communication. Then, if thepresence of an object is determined based on the measured voltage, theaccuracy of the detection of an object decreases. Specifically, forexample, an object may not detected in a case where an object ispresent, or an object may be erroneously detected even though an objectis not present. Then, in a case where this method is applied to thedetection of a foreign substance, the accuracy of the detection of aforeign substance may deteriorate. Even when the measurement target is acurrent, a similar issue arises.

According to various embodiments of the present disclosure, a powertransmission apparatus includes a communication unit configured towirelessly communicate with a power reception apparatus using anantenna, and a power transmission unit configured to wirelessly transmitpower to the power reception apparatus using the antenna. The powertransmission apparatus also includes a measurement unit configured to,in a period during which the transmission of the power from the powertransmission unit is stopped, measure one or both of a voltage and acurrent output from the antenna. The power transmission apparatusfurther includes a first determination unit configured to perform, basedon a measurement result obtained by the measurement performed by themeasurement unit, a determination process for determining that an objectdifferent from the power reception apparatus is present. Additionally,the power transmission apparatus includes a restriction unit configuredto, in a case where it is determined that an object different from thepower reception apparatus is present as a result of the determinationprocess performed by the first determination unit, restrict thetransmission of the power from the power transmission unit, and acontrol unit configured to control the first determination unit not touse in the determination process the measurement result obtained by themeasurement performed by the measurement unit in a period during whichcommunication is performed by the communication unit.

Further features of the present disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of awireless power transmission system.

FIG. 2 is a diagram illustrating an example of a configuration of apower transmission apparatus.

FIG. 3 is a diagram illustrating an example of a configuration of apower reception apparatus.

FIG. 4 is a flowchart illustrating processing executed by a powertransmission apparatus according to a first exemplary embodiment.

FIGS. 5A and 5B are diagrams illustrating a method for measuring aquality factor (a Q factor) according to one embodiment.

FIG. 6 is a flowchart illustrating a foreign substance detection processaccording to the first exemplary embodiment.

FIG. 7 is a flowchart illustrating a foreign substance detection processaccording to a modification of the first exemplary embodiment.

FIG. 8 is a flowchart illustrating a foreign substance detection processaccording to a second exemplary embodiment.

FIG. 9 is a flowchart illustrating a foreign substance detection processaccording to a modification of the second exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments will be described below with reference to thedrawings. It is to be understood that components described in thefollowing description illustrate features of example embodiments of thepresent disclosure, and do not limit the scope of the present inventionto these described example embodiments.

A first exemplary embodiment will be described. FIG. 1 illustrates anexample of the configuration of a wireless charging system (a wirelesspower transmission system) according to the present exemplaryembodiment. As an example, this system includes a power transmissionapparatus 101 and a power reception apparatus 102. Hereinafter, a powerreception apparatus will occasionally be referred to as an “RX”, and apower transmission apparatus will occasionally be referred to as a “TX”.The RX 102 is an electronic device that receives power from the TX 101and charges a built-in battery. The TX 101 is an electronic device thatwirelessly transmits power to the RX 102 placed on a charging stand 103.The RX 102 can receive power from the TX 101 in a range 104. An exampleof the RX 102 is a smartphone, and an example of the TX 101 is anaccessory device for charging the smartphone. Alternatively, each of theRX 102 and the TX 101 may be a storage device such as a hard disk deviceor a memory device, or may be an information processing apparatus suchas a personal computer (PC). Yet alternatively, each of the RX 102 andthe TX 101 may be an image input apparatus such as an imaging apparatus(a camera or a video camera) or a scanner, or may be an image outputapparatus such as a printer, a copying machine, or a projector. Yetalternatively, each of the RX 102 and the TX 101 may have the functionof executing an application other than wireless charging. Yetalternatively, the TX 101 may be a smartphone. In this case, the RX 102may be another smartphone, or may be wireless earphones. Yetalternatively, the RX 102 may be an automobile. Yet alternatively, theTX 101 may be a charger installed in a console in an automobile.

Although a single TX 101 and a single RX 102 are illustrated in thepresent exemplary embodiment, embodiments of the present disclosure canalso be applied to a configuration in which a single TX 101 or differentTXs 101 transmit power to a plurality of RXs 102.

In this system, based on a standard for wireless charging defined by theWireless Power Consortium (WPC) (the WPC standard), wireless powertransmission using an electromagnetic induction method for wirelesscharging is performed. That is, the RX 102 and the TX 101 performwireless power transmission for wireless charging based on the WPCstandard between a power reception coil (a power reception antenna) ofthe RX 102 and a power transmission coil (a power transmission antenna)of the TX 101. The wireless power transmission method is not limited toa method defined by the WPC standard, and may be another electromagneticinduction method, a magnetic field resonance method, an electric fieldresonance method, a microwave method, or a method using a laser.Although wireless power transmission is used for wireless charging inthe present exemplary embodiment, wireless power transmission may beperformed for use other than wireless charging.

The WPC standard defines the magnitude of power guaranteed when the RX102 receives power from the TX 101, as a value termed guaranteed power(hereinafter referred to as “GP”). For example, the GP indicates thepower value of power guaranteed to be output to a load (e.g., a circuitfor charging) in the RX 102 even when the positional relationshipbetween the RX 102 and the TX 101 changes and the power transmissionefficiency between the power reception coil and the power transmissioncoil decreases. For example, in a case where the GP is 5 watts, and evenwhen the positional relationship between the power reception coil andthe power transmission coil changes and the power transmissionefficiency decreases, the TX 101 transmits power by performing controlso that 5 watts can be output to the load in the RX 102.

The RX 102 and the TX 101 according to the present exemplary embodimentperform communication for power transmission/reception control based onthe WPC standard. The communication for power transmission/receptioncontrol will now be described. The WPC standard defines a plurality ofphases including the power transfer phase where power is transmitted,and phases before the power is transmitted. The phases before the poweris transmitted include the (1) selection phase, the (2) ping phase, the(3) identification and configuration phase, the (4) negotiation phase,and the (5) calibration phase. Hereinafter, the identification andconfiguration phase will be referred to as the “I & C phase”.

In the (1) selection phase, the TX 101 intermittently transmits ananalog ping and detects that an object is present in a powertransmittable range (e.g., the power reception apparatus 102 or aconductor piece is placed on the charging stand 103). That is, theanalog ping is a detection signal for detecting the presence of anobject. The TX 101 transmits the analog ping by applying a voltage or acurrent to the power transmission coil. The voltage or the currentapplied to the power transmission coil changes between a case where anobject is placed on the charging stand 103 and a case where an object isnot placed on the charging stand 103. Accordingly, the TX 101 detectsone or both of the voltage value and the current value of the powertransmission coil when the analog ping is transmitted. If the voltagevalue falls below a certain threshold, or if the current value exceeds acertain threshold, the TX 101 determines that an object is present.Then, the TX 101 transitions to the ping phase.

In the (2) ping phase, the TX 101 transmits a digital ping having powergreater than that of the analog ping. The magnitude of the digital pingis sufficient power for a control unit of the RX 102 placed on thecharging stand 103 to start. The RX 102 notifies the TX 101 of themagnitude of a power reception voltage. That is, the RX 102 transmits asignal strength packet (hereinafter referred to as an “SS packet”) tothe TX 101. As described above, the TX 101 receives a response from theRX 102 having received the digital ping, thereby recognizing that theobject detected in the selection phase is the RX 102. When the TX 101receives the notification of the power reception voltage value, the TX101 transitions to the I & C phase.

In the (3) I & C phase, the TX 101 identifies the RX 102 and acquiresdevice configuration information (capability information) from the RX102. To this end, the RX 102 transmits an identification (ID) packet anda configuration packet to the TX 101. The ID packet includesidentification information regarding the RX 102, and the configurationpacket includes device configuration information (capabilityinformation) regarding the RX 102. Receiving the ID packet and theconfiguration packet, the TX 101 responds with an acknowledgement (ACK).Then, the I & C phase ends.

In the (4) negotiation phase, the value of the GP is determined based onthe value of the GP requested by the RX 102 and the power transmissioncapability of the TX 101.

In the (5) calibration phase, based on the WPC standard, the RX 102notifies the TX 101 of a reception power value using a received powerpacket. Then, the TX 101 acquires transmission power corresponding tothe reception power and stores the transmission power in associationwith the reception power. Then, based on at least two pairs of thereception power and the transmission power, the TX 101 calculates andstores parameters for a foreign substance detection process based onpower loss. In the present exemplary embodiment, the TX 101 calculatesand stores parameters for a foreign substance detection process also inthe power transfer phase. Foreign substance detection is the process ofdetermining whether an object (hereinafter referred to as a “foreignsubstance”) different from the RX 102 is present in the powertransmittable range of the TX 101, or there is a possibility that aforeign substance is present in the power transmittable range.

In the power transfer phase, control for starting and continuing thetransmission of power, and stopping the transmission of power due toforeign substance detection and full charge is performed.

The TX 101 and the RX 102 superimpose a signal related to thiscommunication for power transmission/reception control on power based onthe WPC standard and using the same antenna (coil) as wireless powertransmission. Consequently, the TX 101 and the RX 102 can perform thecommunication for power transmission/reception control using the sameantenna (coil) as wireless power transmission. The range where the TX101 and the RX 102 can communicate with each other based on the WPCstandard is almost similar to the power transmittable range. That is, inFIG. 1, the range 104 indicates the range where wireless powertransmission and communication can be performed between the powertransmission coil of the TX 101 and the power reception coil of the RX102.

(Configurations of Apparatuses)

Next, the configurations of the power transmission apparatus 101 (the TX101) and the power reception apparatus 102 (the RX 102) according to thepresent exemplary embodiment will be described. The configurationsdescribed below are merely examples, and part (or all in some cases) ofthe described configurations may be replaced with another configurationthat serves another similar function, or may be omitted, and a furtherconfiguration may be added to the described configurations. Further, asingle block illustrated in the following description may be dividedinto a plurality of blocks, or a plurality of blocks may be integratedinto a single block.

FIG. 2 is a diagram illustrating an example of the configuration of thepower transmission apparatus 101 (the TX 101) according to the presentexemplary embodiment. The TX 101 includes a control unit 201, a powersupply unit 202, a power transmission unit 203, a detection unit 204, apower transmission coil 205, a communication unit 206, an output unit207, an operation unit 208, a memory 209, and a timer 210.

For example, the control unit 201 executes a control program stored inthe memory 209, thereby controlling the entire TX 101. That is, thecontrol unit 201 controls the function units illustrated in FIG. 2. Thecontrol unit 201 performs control regarding power reception control inthe TX 101. As an example, the control unit 201 performs controlrequired for device authentication and power transmission in the TX 101.The control unit 201 may perform control for executing an applicationother than wireless power transmission. The control unit 201 includesone or more processors such as a central processing unit (CPU) and amicroprocessor unit (MPU). The control unit 201 may include hardwarededicated to a specific process, such as an application-specificintegrated circuit (ASIC). Alternatively, the control unit 201 mayinclude an array circuit such as a field-programmable gate array (FPGA)compiled to execute a predetermined process. The control unit 201stores, in the memory 209, information that should be stored during theexecution of various processes. The control unit 201 can measure time ora clock time using the timer 210. In a case where the detection unit 204detects a foreign substance, then, based on the detection of the foreignsubstance, the control unit 201 restricts the power transmission unit203 from transmitting power.

The power supply unit 202 transmits power required for control, powertransmission, and communication to the entire TX 101. The power supplyunit 202 is, for example, commercial power supply or a battery. Thebattery stores power transmitted from mains electricity.

The power transmission unit 203 converts direct current power oralternating current power input from the power supply unit 202 intoalternating current frequency power in a frequency range for use inwireless power transmission. Further, the power transmission unit 203inputs the alternating current frequency power to the power transmissioncoil 205, thereby generating an electromagnetic wave with which to causethe RX 102 to receive power. The frequency of the alternating currentpower generated by the power transmission unit 203 is approximatelyseveral hundreds of kilohertz (e.g., 110 kHz to 205 kHz).

Based on an instruction from the control unit 201, the powertransmission unit 203 inputs alternating current frequency power to thepower transmission coil 205 to cause the power transmission coil 205 tooutput an electromagnetic wave with which to transmit power to the RX102. The power transmission unit 203 adjusts a voltage (a powertransmission voltage) or a current (a power transmission current) to beinput to the power transmission coil 205, thereby controlling theintensity of the electromagnetic wave to be output. The intensity of theelectromagnetic wave becomes strong if the power transmission voltage orthe power transmission current is made great. The intensity of theelectromagnetic wave becomes weak if the power transmission voltage orthe power transmission current is made small. Based on an instructionfrom the control unit 201, the power transmission unit 203 controls theoutput of the alternating current frequency power so that thetransmission of power from the power transmission coil 205 is started orstopped. The power transmission unit 203 of the TX 101 according to thepresent exemplary embodiment includes a switch on a circuit connected tothe power transmission coil 205. When a quality factor (a Q factor) ismeasured, the power transmission unit 203 switches the switch inside thepower transmission unit 203 and disconnects the connection with thepower transmission coil 205, thereby stopping the application of thevoltage to the power transmission coil 205. The switch may be located ata position other than inside the power transmission unit 203. Forexample, the switch may be provided between the power transmission unit203 and the detection unit 204 or between the detection unit 204 and thepower transmission coil 205 in FIG. 2.

The detection unit 204 measures the voltage or the current of the powertransmission coil 205, thereby detecting whether an object is present inthe range 104. The detection unit 204 detects, for example, the voltageor the current of the power transmission coil 205 when the powertransmission unit 203 transmits power with an analog ping in accordancewith the WPC standard via the power transmission coil 205. If thevoltage falls below a predetermined voltage value, or if the currentvalue exceeds a predetermined current value, the detection unit 204 candetermine that an object is present in the range 104. Then, thedetermination of whether this object is the RX 102 or a foreignsubstance other than the RX 102 is made. Specifically, if apredetermined response to a digital ping subsequently transmitted fromthe communication unit 206 is received, it is determined that thisobject is the RX 102. When the Q factor is acquired, the detection unit204 measures the voltage of the power transmission coil 205. Then, usingthe Q factor acquired based on the measurement result, the detectionunit 204 performs a determination process for determining whether aforeign substance is present in the power transmittable range (foreignsubstance detection). The details will be described below.

The communication unit 206 performs the above control communicationbased on the WPC standard with the RX 102. The communication unit 206modulates an electromagnetic wave output from the power transmissioncoil 205 and transmits information to the RX 102. The communication unit206 demodulates an electromagnetic wave output from the powertransmission coil 205 and modulated by the RX 102, thereby acquiringinformation transmitted from the RX 102. That is, the communicationperformed by the communication unit 206 is superimposed on thetransmission of power from the power transmission coil 205.

The output unit 207 provides information to a user by any technique suchas a visual, auditory, or tactile technique. For example, the outputunit 207 notifies the user of information indicating the state of the TX101 or the state of the wireless power transmission system including theTX 101 and the RX 102 in FIG. 1. For example, the output unit 207includes a liquid crystal display or a light-emitting diode (LED), aloudspeaker, a vibration generation circuit, and another notificationdevice.

The operation unit 208 has a reception function for receiving anoperation of the user on the TX 101. For example, the operation unit 208includes a button, a keyboard, a sound input device such as amicrophone, a motion detection device such as an acceleration sensor ora gyro sensor, and another input device. A device obtained byintegrating the output unit 207 and the operation unit 208 as in a touchpanel may be used.

The memory 209 stores various pieces of information. The memory 209 maystore information obtained by a function unit different from the controlunit 201. The timer 210 measures time using, for example, a count uptimer that measures the time elapsed from the clock time when the countup timer is started, or a count down timer that counts down from a settime.

FIG. 3 is a diagram illustrating an example of the configuration of thepower reception apparatus 102 (the RX 102) according to the presentexemplary embodiment. The RX 102 includes a control unit 301, a battery302, a power reception unit 303, a detection unit 304, a power receptioncoil 305, a communication unit 306, an output unit 307, an operationunit 308, a memory 309, a timer 310, and a charging unit 311.

The control unit 301 executes a control program stored in the memory309, for example, thereby controlling the entire RX 102. As an example,the control unit 301 performs control required for device authenticationand power reception in the RX 102. The control unit 301 may performcontrol for executing an application other than wireless powertransmission. The control unit 301 includes one or more processors suchas a CPU and an MPU. The control unit 201 may include hardware dedicatedto a specific process, such as an ASIC, or an array circuit such as anFPGA compiled to execute a predetermined process. The control unit 301stores, in the memory 309, information that should be stored during theexecution of various processes. The control unit 301 can measure timeusing the timer 310.

The battery 302 transmits power required for control, power reception,and communication to the entire RX 102. The battery 302 stores powerreceived via the power reception coil 305. In the power reception coil305, an induced electromotive force is generated by an electromagneticwave emitted from the power transmission coil 205 of the TX 101, and thepower reception unit 303 acquires power generated in the power receptioncoil 305.

The power reception unit 303 acquires alternating current powergenerated by electromagnetic induction in the power reception coil 305.Then, the power reception unit 303 converts the alternating currentpower into direct current power or alternating current power of apredetermined frequency and outputs the power to the charging unit 311that performs a process for charging the battery 302. That is, the powerreception unit 303 transmits the power to a load in the RX 102. Theabove GP is the amount of power guaranteed to be output from the powerreception unit 303.

The detection unit 304 detects whether the RX 102 is placed in the range104 where the RX 102 can receive power from the TX 101. The detectionunit 304 detects, for example, the voltage or the current of the powerreception coil 305 when the power reception unit 303 receives power witha digital ping in accordance with the WPC standard via the powerreception coil 305. If the detected voltage falls below a predeterminedvoltage threshold, or if the detected current value exceeds apredetermined current threshold, for example, the detection unit 304 candetermine that the RX 102 is placed in the range 104.

The communication unit 306 performs the above-described controlcommunication based on the WPC standard with the TX 101 throughcommunication for superimposing a signal based on the WPC standard andusing the same antenna (coil) as wireless power transmission. Thecommunication unit 306 demodulates an electromagnetic wave input fromthe power reception coil 305, thereby acquiring information transmittedfrom the TX 101. The communication unit 306 further performs loadmodulation on the electromagnetic wave, thereby superimposinginformation that should be transmitted to the TX 101 on theelectromagnetic wave. Consequently, the communication unit 306communicates with the TX 101. That is, the communication performed bythe communication unit 306 is superimposed on the transmission of powerfrom the power transmission coil 205 of the TX 101 (FIG. 2).

The output unit 307 provides information to the user by any techniquesuch as a visual, auditory, or tactile technique. For example, theoutput unit 307 notifies the user of the state of the RX 102 or thestate of the wireless power transmission system including the TX 101 andthe RX 102 in FIG. 1. For example, the output unit 307 includes a liquidcrystal display or an LED, a loudspeaker, a vibration generationcircuit, and another notification device.

The operation unit 308 has a reception function for receiving anoperation of the user on the RX 102. For example, the operation unit 308includes a button, a keyboard, a sound input device such as amicrophone, a motion detection device such as an acceleration sensor ora gyro sensor, and another input device. A device obtained byintegrating the output unit 307 and the operation unit 308 as in a touchpanel may be used.

The memory 309 stores various pieces of information. The memory 309 maystore information obtained by a function unit different from the controlunit 301. The timer 310 measures time using, for example, a count uptimer that measures the time elapsed from the clock time when the countup timer is started, or a count down timer that counts down from a settime.

Next, a description will be given of processing performed by the powertransmission apparatus 101 (the TX 101) and the power receptionapparatus 102 (the RX 102) according to the present exemplary embodimentwith reference to the drawings.

<Flowchart of Power Transmission Apparatus>

Next, the operation of the power transmission apparatus 101 (the TX 101)according to the present exemplary embodiment will be described withreference to FIG. 4. Processing illustrated in FIG. 4 is achieved by thecontrol unit 201 of the TX 101 executing a control program stored in thememory 209, calculating information, processing information, andcontrolling pieces of hardware.

In step F401, the control unit 201 executes processes defined as theselection phase and the ping phase in the WPC standard. Then, forexample, the RX 102 detects a digital ping from the TX 101, therebydetecting that the RX 102 is placed on the charging stand 103 of the TX101. Then, if the RX 102 detects the digital ping, the RX 102 transmitsan SS packet including the value of a received voltage to the TX 101.The TX 101 detects that the RX 102 is placed in the power transmittablerange of the TX 101.

In step F402, the control unit 201 performs communication in the I & Cphase via the communication unit 206, thereby acquiring identificationinformation and capability information from the RX 102. Theidentification information regarding the RX 102 can include amanufacturer code and a basic device ID. The capability informationregarding the RX 102 can include information that allows the specifyingof a version of the WPC standard the RX 102 is compliant with, a maximumpower value indicating the maximum value of power that can be receivedby the RX 102, and information indicating whether the RX 102 has thenegotiation function according to the WPC standard. The TX 101 mayacquire the identification information and the capability informationregarding the RX 102 by a method other than the communication in the I &C phase. The identification information may include information thatallows the identification of the individuality of the RX 102, such as awireless power ID. As described above, the identification informationmay include information other than the above. Similarly, the capabilityinformation may also include information other than the above.

In step F403, the control unit 201 performs communication in thenegotiation phase via the communication unit 206, thereby determiningthe value of the GP based on the value of the GP requested by the RX102.

In step F404, the control unit 201 starts a process in the calibrationphase (hereinafter referred to as a “calibration process”). Thecalibration process is the process of, regarding power transmitted fromthe TX 101 to the RX 102, calibrating the correlation between the valueof the power measured inside the TX 101 (transmission power) and thevalue of the power measured inside the RX 102 (reception power). In thecalibration phase, the TX 101 transmits power for communicatinginformation and acquiring the above correlation between the values ofthe power in the calibration process.

The processes of steps F404 to F407 are processes performed in thecalibration phase. In these processes, the calculation of a Q factor toconfirm that a foreign substance is not present in the powertransmittable range, and foreign substance detection based on thecalculated Q factor are performed. The TX 101 according to the presentexemplary embodiment calculates the Q factor as a parameter for use inforeign substance detection. A method for measuring the Q factor in thetime domain will be described with reference to FIG. 5A. A waveformillustrated in FIG. 5A indicates changes over time in the measured valueof a voltage (hereinafter referred to as the “voltage value”) inside thepower transmission coil 205 of the TX 101. The horizontal axisrepresents time, and the vertical axis represents the voltage value. Awaveform 500 indicates the voltage value of a high-frequency voltageapplied to the power transmission coil 205. A clock time T0 indicatesthe clock time when the application of the high-frequency voltage to thepower transmission coil 205 is stopped. A point 501 is a part of theenvelope of the voltage value indicated by the waveform 500. Coordinates(T1, A1) corresponding to the point 501 indicate that the voltage valueat a clock time T1 is A1. Similarly, a point 502 is a part of theenvelope of the voltage value indicated by the waveform 500, andcoordinates (T2, A2) corresponding to the point 502 indicate that thevoltage value at a clock time T2 is A2.

The Q factor is measured based on a change in the voltage value afterthe application of the high-frequency voltage to the power transmissioncoil 205 is stopped. In the example illustrated in FIG. 5A, the Q factoris acquired by measuring the amount of change in the voltage value afterthe clock time T0. In FIG. 5A, for example, the voltage values A1 and A2at the clock times T1 and T2, respectively, which are clock times in aperiod after the clock time T0 when the application of thehigh-frequency voltage is stopped, are measured. Based on these clocktimes and measured voltages, the Q factor is calculated by equation 1.

Q=ω(T2−T1)/2 ln(A1/A2)  (equation 1)

As described above, the Q factor is calculated based on the length oftime from the clock time T1 to the clock time T2 and the ratio of thevoltage value A1 corresponding to the clock time T1 to the voltage valueA2 corresponding to the clock time T2. In equation 1, w represents theangular velocity of the high-frequency voltage (obtained by multiplyingthe frequency by 2n).

Next, a process for measuring the Q factor by the TX 101 according tothe present exemplary embodiment will be described with reference toFIG. 5B. A waveform 503 indicates a high-frequency voltage applied fromthe power transmission unit 203 to the power transmission coil 205, andthe frequency of the high-frequency voltage is a frequency between 110kHz and 148.5 kHz, which is used in the WPC standard. In the period froma clock time T0 to a clock time T5, the power transmission unit 203switches the switch and disconnects the connection with the powertransmission coil 205, thereby stopping the application of thehigh-frequency voltage. The period from the clock time T0 to the clocktime T5 is a period extremely short compared to the period during whichthe TX 101 transmits power to the RX 102.

Points 504 and 505 are parts of the envelope of the voltage valueindicated by the waveform 503. The power transmission unit 203 stops thetransmission of power in the period from the clock time T0 to the clocktime T5, and the detection unit 204 measures the voltage value at aclock time T3 in this period and a clock time T4 after a predeterminedtime elapses from the clock time T3. In the example illustrated in FIG.5B, the voltage value at the clock time T3 and the voltage value at theclock time T4 are A3 and A4, respectively. Using the clock time T3, theclock time T4, the voltage value A3, the voltage value A4, and theangular velocity of the high-frequency voltage, the TX 101 calculatesthe Q factor by equation 1. As described above, the detection unit 204of the TX 101 measures the voltage value in the state where the powertransmission unit 203 has stopped the transmission of power to the RX102. Then, the detection unit 204 calculates the Q factor. The TX 101switches the switch in the power transmission unit 203 at the clock timeT5 and resumes the transmission of power.

The TX 101 according to the present exemplary embodiment acquires the Qfactor by the above-described method. Based on the acquired Q factor,the TX 101 performs foreign substance detection and confirms that aforeign substance is not present in the power transmittable range. Atthis time, the TX 101 stores the Q factor measured in the state where aforeign substance is not present in the power transmittable range, as areference value Qx in advance. If power is transmitted in a case where aforeign substance such as a conductor piece is present in the powertransmittable range, not only the RX 102 but also the foreign substanceconsumes power. Consequently, it is assumed that in a case where aforeign substance is present, the voltage value when the TX 101 stopsthe transmission of power attenuates more than in a case where a foreignsubstance is not present. Consequently, it is assumed that the value ofthe Q factor based on equation 1 in a case where a foreign substance ispresent is smaller than that of the Q factor in a case where a foreignsubstance is not present. Thus, based on the fact that the acquired Qfactor is smaller than the reference value Qx, the TX 101 determinesthat a foreign substance is present (detects a foreign substance). Atthis time, the TX 101 calculates the difference between the acquired Qfactor and the reference value Qx. If the difference is greater than apredetermined threshold Th, the TX 101 determines that a foreignsubstance is present. If the difference between the acquired Q factorand the reference value Qx is smaller than the predetermined thresholdTh, the TX 101 can confirm that a foreign substance is not present inthe power transmittable range.

That is, if the following inequality 2 holds regarding the measured Qfactor, the TX 101 determines that a foreign substance is present.

Q≤Qx−Th  (inequality 2)

The communication unit 206 of the TX 101 according to the presentexemplary embodiment modulates or demodulates an electromagnetic wavegenerated by the voltage applied from the power transmission unit 203 tothe power transmission coil 205, thereby communicating information withthe RX 102. The communication unit 306 of the RX 102 performs loadmodulation on an electromagnetic wave received by the power receptioncoil 305, thereby communicating information with the TX 101. Thus, ifthe voltage value is measured while the communication unit 206 and thecommunication unit 306 are in communication with each other, a voltagevalue appropriate for the acquisition of the Q factor for use in theforeign substance detection may not be measured. For example, if loadmodulation is performed in the period from the clock time T0 to theclock time T5 when the TX 101 stops the application of the voltage inFIG. 5B, there is a possibility that the voltage value changes comparedto a case where load modulation is not performed. Consequently, there isa possibility that the values of the voltages A3 and A4 at the clocktimes T3 and T4 in a case where load modulation is performed are greateror smaller than the voltage values in a case where load modulation isnot performed. If the Q factor acquired based on these voltage values isused in the foreign substance detection, there is a possibility that aforeign substance is not detected in a case where a foreign substance ispresent, or a foreign substance is erroneously detected in a case wherea foreign substance is not present.

For the above reason, for example, in a case where foreign substancedetection is performed based on the Q factor obtained by a singlemeasurement, and if this single measurement is performed in the periodduring which the TX 101 and the RX 102 are in communication with eachother, there is a possibility that the foreign substance detectioncannot be performed with high accuracy. Thus, the TX 101 according tothe present exemplary embodiment calculates the Q factor multiple timesfor the foreign substance detection, and based on each of themeasurement results, determines whether a foreign substance is present.In the following description, the measurement of the voltage value forcalculating the Q factor and the calculation of the Q factor based onthe measured voltage value will occasionally be referred to collectivelyas “the measurement of the Q factor”.

A foreign substance detection process based on the measurement of the Qfactor according to the present exemplary embodiment will be describedwith reference to FIG. 6. FIG. 6 is a flowchart illustrating theoperation of the foreign substance detection process in the powertransmission apparatus 101 (the TX 101), and this process corresponds tosteps F406 and F412 in FIG. 4. In step F601, the TX 101 according to thepresent exemplary embodiment measures the Q factor a predeterminednumber of times set in advance. In this case, the predetermined numberof times is set to five times. In the following description, thepredetermined number of times the Q factor is measured will be referredto as “the number of measurement times”.

In step F602, the control unit 201 of the TX 101 controls the powertransmission unit 203 to stop the application of the voltage to thepower transmission coil 205. The detection unit 204 measures the voltagevalue in the period during which the application of the voltage isstopped. The control unit 201 controls the communication unit 206 of theTX 101 not to transmit a signal when the voltage value is measured.Based on the measured value of the voltage, the detection unit 204calculates the Q factor. After stopping the application of the voltageand measuring the voltage value, the TX 101 resumes the application ofthe voltage. The TX 101 defines, as a single measurement of the Qfactor, a measurement process for stopping the application of thevoltage, measuring the voltage value at different timings (the clocktimes T3 and T4 in FIG. 5B), and resuming the application of thevoltage. Then, the TX 101 repeatedly performs this measurement of the Qfactor the number of measurement times. When the TX 101 repeatedlyperforms this measurement of the Q factor, in step F603, from themeasurement of the Q factor to the next measurement of the Q factor, theTX 101 waits a random time for the execution of the next measurement ofthe Q factor within a predetermined time interval (e.g., 10 msec to 50msec). The TX 101 repeats the processes of step F602 and F603 the numberof measurement times. Consequently, a plurality of measurements of the Qfactor is executed at random time intervals. In the example of FIG. 6,every time the single measurement process is performed, the Q factor iscalculated. Embodiments of the present disclosure, however, are notlimited to this implementation. The TX 101 can also perform a processfor stopping the application of the voltage, measuring the voltage valueat different timings, and resuming the application of the voltage fivetimes, and then calculate the Q factor based on each measured value, forexample, in other embodiments. That is, the calculation of the Q factormay be performed after the application of the voltage is resumed in someembodiments. In view of the possibility that a foreign substance ispresent, however, it is possible to detect the presence of a foreignsubstance earlier and respond to the foreign substance more quickly ifthe Q factor is calculated while the application of the voltage isstopped.

In step F604, regarding each of Q factors obtained by measuring the Qfactor the predetermined number of times (five times in this case),using inequality 2, the detection unit 204 determines whether thedifference between the measured Q factor and the reference value Qxexceeds the threshold Th. If the number of measured Q factors thedifference of which from the reference value Qx exceeds the threshold This greater than or equal to a certain number (YES in step F604), then instep F605, the detection unit 204 determines that a foreign substance ispresent in the power transmittable range of the TX 101. If the number ofmeasured Q factors the difference of which from the reference value Qxexceeds the threshold Th is less than the certain number (NO in stepF604), then in step F606, the detection unit 204 determines that aforeign substance is not present in the power transmittable range of theTX 101. In the example of FIG. 6, the certain number is set to four.

By the above processing, the TX 101 can detect a foreign substance basedon a plurality of measurement results of the Q factor. Consequently,even when any of the plurality of measurements of the Q factor isperformed in the period during which the TX 101 and the RX 102 are incommunication with each other, it is possible to prevent erroneousforeign substance detection from being performed by taking othermeasurement results into account.

Referring back to FIG. 4, in step F407, if a foreign substance isdetected in the foreign substance detection process in step F406 (YES instep F407), then in step F415, the TX 101 stops the transmission ofpower. If a foreign substance is not detected in the foreign substancedetection process in step F406 (NO in step F407), then in step F408, thecalibration process is ended.

In step F409, the TX 101 transitions to the power transfer phase andstarts the process of transmitting power for charging to the RX 102.After starting the transmission of power, the TX 101 continues thetransmission of power until an end power transfer packet (hereinafterreferred to as an “EPT”) as a notification for stopping the transmissionof power is transmitted from the RX 102. In a case where the TX 101receives the EPT (YES in step F410), then in step F415, the TX 101 stopsthe transmission of power.

If the TX 101 has not received the EPT (NO in step F410), then in stepF411, the TX 101 determines whether a predetermined time (hereinafterreferred to as a “timeout time”) has elapsed since the foreign substancedetection process has been executed. If the timeout time has elapsedsince the foreign substance detection process has been performed mostrecently, the TX 101 performs the foreign substance detection processagain and thereby can periodically confirm whether a new foreignsubstance is placed in the power transmittable range. If the timeouttime has not elapsed (NO in step F411), the TX 101 executes the processof step F410 again. If the timeout time has elapsed (YES in step F411),then in step F412, the TX 101 executes the foreign substance detectionprocess based on the measurement of the Q factor. The foreign substancedetection process performed at this time is a process similar to that ofstep F406.

In the power transfer phase, in step F412, the foreign substancedetection based on the measurement of the Q factor is performed, and instep F413, foreign substance detection based on power loss areperformed. The foreign substance detection based on power loss is theprocess of, if the value of power transmitted from the TX 101 is lostmore than a predetermined amount, determining that a foreign substanceis present. The foreign substance detection based on power loss isperformed by notifying the TX 101 of power received by the RX 102. Theforeign substance detection based on power loss can be executed afterthe calibration phase is completed, and can be executed at any timingbetween steps F410 and F414. For example, the foreign substancedetection based on power loss may be executed at the same timing as or adifferent timing from the foreign substance detection based on themeasurement of the Q factor. The order of steps F412 and F413 may bereversed.

A description will be given of the combined use of the foreign substancedetection based on the measurement result of the Q factor and theforeign substance detection based on power loss. If both the result ofthe foreign substance detection based on the measurement result of the Qfactor and the result of the foreign substance detection based on powerloss indicate “a foreign substance is not present”, the TX 101determines that a foreign substance is not present. If, on the otherhand, at least one of the result of the foreign substance detectionbased on the measurement result of the Q factor and the result of theforeign substance detection based on power loss indicates “a foreignsubstance is present”, the TX 101 determines that (there is a highpossibility that) a foreign substance is present. Consequently, it ispossible to prevent the TX 101 from erroneously determining that aforeign substance is not present in a case where a foreign substance ispresent, and transmitting power.

If the result of the foreign substance detection based on themeasurement result of the Q factor and the result of the foreignsubstance detection based on power loss are different from each other,the TX 101 may give priority to either one of the results of the foreignsubstance detection methods. For example, suppose that in a case wherepriority is given to the result of the foreign substance detection basedon power loss, it is determined that “a foreign substance is notpresent” in the foreign substance detection based on the measurementresult of the Q factor, and it is determined that “a foreign substanceis present” in the foreign substance detection based on power loss. Inthis case, by giving priority to the result of the foreign substancedetection based on power loss, the TX 101 determines that “a foreignsubstance is present”. Similarly, priority may be given to the result ofthe foreign substance detection based on the measurement result of the Qfactor. In the above method in which if it is determined that “a foreignsubstance is present” in at least one of a plurality of foreignsubstance detection methods, the TX 101 determines that “a foreignsubstance is present”, the TX 101 is prevented from transmitting powerwhen a foreign substance is present. In this method, however, there isalso a possibility that the transmission of power is frequentlyrestricted. Thus, in a case where a plurality of foreign substancedetection methods is employed, it is determined in advance which of theresults of the foreign substance detection methods priority is given to,whereby it can be expected that the transmission of power is notfrequently restricted. It is not necessary to adopt a configuration inwhich both steps F412 and F413 are always executed. Alternatively, aconfiguration may be adopted in which at least one of steps F412 andF413 is executed.

If a foreign substance is not detected in the above foreign substancedetection processes (NO in step F414), the TX 101 executes the processesof step F410 and the subsequent steps again. If a foreign substance isdetected (YES in step F414), then in step F415, the TX 101 stops thetransmission of power.

As described above, when the foreign substance detection based on themeasurement of the Q factor is performed, the TX 101 determines whethera foreign substance is present based on a plurality of measurements ofthe Q factor. In this way, if any of the plurality of measurements ofthe Q factor is performed in the period during which the TX 101 and theRX 102 are in communication with each other, it is possible to preventerroneous foreign substance detection from being performed by takingother measurement results into account. In a case where the foreignsubstance detection based on the measurement of the Q factor and theforeign substance detection based on power loss are performed incombination, the TX 101 can perform more reliable foreign substancedetection. As the processing of the TX 101 in a case where a foreignsubstance is detected, the transmission of power may be restricted sothat the transmission of power is stopped as described above, or thetransmission of power may be restricted so that the transmission poweris smaller than at the time when a foreign substance is not detected.

Alternatively, as the processing in a case where a foreign substance isdetected, a configuration may be adopted in which the GP is determinedagain between the TX 101 and the RX 102. If the TX 101 determines thatthe RX 102 has the capability to renegotiate for the GP, the TX 101transmits a signal instructing the RX 102 to renegotiate for determiningthe GP again. At this time, the TX 101 may notify the RX 102 of thenegotiable maximum value of the GP. The negotiable maximum value of theGP may be limited to 5 W. If the TX 101 determines that the RX 102 doesnot have the capability to renegotiate for the GP, the TX 101 performsthe process of restricting the transmission of power so that thetransmission power is smaller than at the time when a foreign substanceis not detected, or changing the value of the transmission power to apredetermined value (e.g., 5 W), or stopping the transmission of power.

A description will be given of the effect of the foreign substancedetection based on the measurement of the Q factor on the foreignsubstance detection based on power loss. The foreign substance detectionbased on power loss cannot be executed unless the processes in thecalibration phase for calculating parameters for use in the foreignsubstance detection are completed. That is, the foreign substancedetection based on power loss cannot be used in the calibration phase.If a foreign substance is present in the power transmittable range atthe stage of the calibration phase, there is a possibility that aninappropriate parameter is acquired and the accuracy of the foreignsubstance detection based on power loss in the subsequent power transferphase decreases. In contrast, the foreign substance detection based onthe measurement result of the Q factor can be executed even in thecalibration phase. Thus, it can be determined whether a foreignsubstance is present at the stage of the calibration phase.Consequently, the TX 101 can determine that a foreign substance ispresent at the stage of the calibration phase, and restrict thetransmission of power.

A modification of the first exemplary embodiment will be described. Theconfiguration of a wireless charging system and the configurations ofapparatuses in the wireless charging system are similar to those in thefirst exemplary embodiment, and therefore description thereof will beomitted. FIG. 7 is a flowchart illustrating a foreign substancedetection process performed by the power transmission apparatus 101 (theTX 101) according to the modification of the first exemplary embodiment.The TX 101 according to this modification executes processing similar tothe processing illustrated in FIG. 4, but executes processingillustrated in FIG. 7 in the foreign substance detection in steps F406and F412. Description of a processing content similar to that in FIG. 4will be omitted.

In step F701, similarly to the first exemplary embodiment, the TX 101makes a setting to measure the Q factor a predetermined number ofmeasurement times. In this case, the number of measurement times is setto five times. In step F702, the TX 101 measures the Q factor. Themethod for measuring the Q factor is similar to that in the firstexemplary embodiment, and therefore description thereof will be omitted.After the TX 101 measures the Q factor, the TX 101 determines whetherthe difference between the measured Q factor and the reference value Qxexceeds the threshold Th. If the difference exceeds the threshold Th(YES in step F703), then in step F704, regarding Q factors acquired thusfar by measuring the Q factor the number of measurement times (fivetimes in this case), the TX 101 determines whether the difference fromthe reference value Qx exceeds the threshold Th as many times insuccession as a predetermined number of times. In the followingdescription, the predetermined number of times at this time will bereferred to as “the number of successive times”. The number ofsuccessive times regarding the measurement result of the Q factor thedifference of which from the reference value Qx exceeds the threshold This defined as a first number of successive times. The number ofsuccessive times regarding the measurement result of the Q factor thedifference of which from the reference value Qx does not exceed thethreshold Th is defined as a second number of successive times. In theexample of FIG. 7, the first number of successive times is four times,and the second number of successive times is twice.

In a case where the Q factor is measured at random time intervals, andif a plurality of Q factors the difference of which from the referencevalue Qx exceeds the threshold Th is obtained in succession, it isassumed that there is a high possibility that a foreign substance ispresent. Thus, if the difference between the measured Q factor and thereference value Qx exceeds the threshold Th as many times in successionas the first number of times (YES in step F704), then in step F708, theTX 101 determines that a foreign substance is present. At this time,even when the number of times the Q factor is measured is less than thenumber of measurement times, it is determined that a foreign substanceis present. For example, if the number of times the Q factor is measuredis four times and the difference from the reference value Qx exceeds thethreshold Th regarding all the Q factors obtained by the respectivemeasurements, it is determined that a foreign substance is present atthis time. If Q factors the difference of which from the reference valueQx does not exceed the threshold Th are not obtained as many times insuccession as the first number of successive times (NO in step F704),and if the number of times the Q factor is measured is less than thefirst number of successive times, then in step F706, the TX 101 waits arandom time for the execution of the next measurement of the Q factor.The TX 101 repeats the measurement of the Q factor until the Q factor ismeasured the number of measurement times.

If the difference does not exceed the threshold Th in step F703 (NO instep F703), then in step F705, regarding Q factors acquired thus far bymeasuring the Q factor the number of measurement times, the TX 101determines whether the difference from the reference value Qx does notexceed the threshold Th as many times in succession as the second numberof successive times. In a case where the Q factor is measured at randomtime intervals, and if a plurality of Q factors the difference of whichfrom the reference value Qx does not exceed the threshold Th is obtainedin succession, it is assumed that there is a high possibility that aforeign substance is not present. Thus, if Q factors the difference ofwhich from the reference value Qx does not exceed the threshold Th areobtained as many times in succession as the second number of successivetimes (YES in step F705), then in step F709, the TX 101 determines thata foreign substance is not present. At this time, even when the numberof times the Q factor is measured is less than the number of measurementtimes, it is determined that a foreign substance is not present. If Qfactors the difference of which from the reference value Qx does notexceed the threshold Th are not obtained as many times in succession asthe second number of successive times (NO in step F705), and if thenumber of times the Q factor is measured is less than the second numberof successive times, then in step F706, the TX 101 waits a random timefor the execution of the next measurement of the Q factor. The TX 101repeats the measurement of the Q factor until the Q factor is measuredthe number of measurement times.

If the determination is not YES in steps F704 and F705, and the Q factoris measured the number of measurement times, the TX 101 executes theprocess of step F707. The processes of step F707 to F709 are similar tothe processes of steps F604 to F606 in the first exemplary embodiment,and therefore description thereof will be omitted. For example, in acase where the Q factor is measured five times, and if the obtainedresults of determining whether the difference between the measured Qfactor and the reference value Qx exceeds the threshold Th are“exceeds”, “exceeds”, “does not exceed”, “exceeds”, and “exceeds” inthis order, the process of step F707 is executed. In this example, sincethe difference exceeds the threshold Th the certain number of times(four times in this case) or more (YES in step F707), in step F708, itis determined that a foreign substance is present.

As described above, regarding the measured Q factor, the TX 101according to this modification determines whether the difference fromthe reference value Qx exceeds the threshold Th as many times insuccession as a predetermined number of times. The TX 101 performs theprocesses of steps F704 and F705, whereby, in a case where similarmeasured Q factors are obtained in succession, the TX 101 can reduce thenumber of times the Q factor is measured. Consequently, it is possibleto reduce the processing load of the TX 101 related to foreign substancedetection. In the above modification, a case has been described wherethe first number of successive times and the certain number are equal toeach other. The second number of successive times is obtained by (thenumber of measurement times—the first number of successive times+1).Embodiments of the present disclosure, however, are not limited to thisconfiguration. The TX 101 can independently set each of the first numberof successive times and the second number of successive times to anyvalue in other embodiments. For example, the TX 101 may set both thefirst number of successive times and the second number of successivetimes to four times. That is, it is possible to set the first number ofsuccessive times and the second number of successive times to any valuesless than or equal to the number of measurement times in someembodiments.

If a plurality of measured Q factors includes a certain number of Qfactors the difference of which from the reference value Qx exceeds thethreshold Th, the TX 101 according to each of the first exemplaryembodiment and the modification of the first exemplary embodimentdetermines that a foreign substance is present. Embodiments of thepresent disclosure, however, are not limited to this. Alternatively, forexample, if the ratio of the number of Q factors the difference of whichfrom the reference value Qx exceeds the threshold Th to the number ofmeasurement times set in advance is a certain ratio or more, the TX 101may determine that a foreign substance is present. In addition,alternatively, if the number of Q factors the difference of which fromthe reference value Qx does not exceed the threshold Th is a certainnumber or more, the TX 101 may determine that a foreign substance is notpresent. Yet alternatively, the TX 101 may compare the number of Qfactors the difference of which from the reference value Qx exceeds thethreshold Th and the number of Q factors the difference of which fromthe reference value Qx does not exceed the threshold Th, and based onthe results of the greater number of Q factors, the TX 101 may make adetermination. In the above-described first exemplary embodiment and themodification of the first exemplary embodiment, the TX 101 measures theQ factor a predetermined number of times (the number of measurementtimes). Alternatively, the TX 101 may repeatedly measure the Q factor,for example, until a predetermined time elapses.

A second exemplary embodiment will be described. In the presentexemplary embodiment, a description is given of the TX 101 thatdetermines, in a case where the Q factor is measured for foreignsubstance detection, whether to use the measured Q factor in the foreignsubstance detection. The configuration of a wireless charging system andthe configurations of apparatuses in the wireless charging system aresimilar to those in the first exemplary embodiment, and thereforedescription thereof will be omitted. FIG. 8 is a flowchart illustratinga foreign substance detection process performed by the powertransmission apparatus 101 (the TX 101) according to the secondexemplary embodiment. The TX 101 according to the present exemplaryembodiment executes processing similar to the processing illustrated inFIG. 4, but executes processing illustrated in FIG. 8 in the foreignsubstance detection in steps F406 and F412. Description of a processingcontent similar to that in FIG. 4 will be omitted.

In step F801, the TX 101 measures the Q factor. The method for measuringthe Q factor is similar to that in the first exemplary embodiment, andtherefore description thereof will be omitted. In step F802, the TX 101determines whether communication was performed at the timing when thevoltage value of the power transmission coil 205 was measured tocalculate the Q factor. The determination of whether communication wasperformed is made by determining whether a signal transmitted from theRX 102 is superimposed on the voltage in the period from the clock timeT0 to the clock time T5 in the example of FIG. 5B. The communicationunit 206 demodulates an electromagnetic wave generated in the powertransmission coil 205 in the period from the clock time T0 to the clocktime T5. Then, if a signal transmitted from the RX 102 is superimposedon the electromagnetic wave, the TX 101 determines that communicationwas performed in the period during which the application of the voltagewas stopped. Thus, the communication unit 206 can determine thatcommunication was performed at the timing when the voltage value of thepower transmission coil 205 was measured.

If the voltage value of the power transmission coil 205 is measured inthe period during which communication is performed, a voltage valueappropriate for the acquisition of the Q factor for use in the foreignsubstance detection may not be measured. Thus, if it is determined thatcommunication was performed during the measurement of the voltage value(YES in step F802), there is a possibility that the measured voltagevalue is inappropriate for the calculation of the Q factor for use inthe foreign substance detection, and therefore, in step F801, the TX 101measures the Q factor again. If it is determined that communication wasnot performed during the measurement of the voltage value (NO in stepF802), the TX 101 determines that the measured voltage value isappropriate for the calculation of the Q factor for use in the foreignsubstance detection. Then, in step F803, the TX 101 performs adetermination process in the foreign substance detection. In step F803,the TX 101 determines whether the difference between the measured Qfactor and the reference value Qx exceeds the threshold Th. If it isdetermined that the difference exceeds the threshold Th (YES in stepF803), then in step F804, the TX 101 determines that a foreign substanceis present. If it is determined that the difference does not exceed thethreshold Th (NO in step F803), then in step F805, the TX 101 determinesthat a foreign substance is not present.

As described above, if communication was performed at the timing whenthe voltage value of the power transmission coil 205 was measured tocalculate the Q factor, the TX 101 according to the present exemplaryembodiment does not use the Q factor based on this measured value inforeign substance detection, and measures the voltage value again. Withthis configuration, a voltage value likely to be inappropriate for aforeign substance detection process is not used. Thus, it is possible toprevent a decrease in the accuracy of the foreign substance detectionprocess. While FIG. 8 illustrates an example of the processing in whichthe measurement of the voltage value of the power transmission coil 205and the calculation of the Q factor based on the voltage value areperformed in step F801, the calculation of the Q factor based on thevoltage value may be performed after step F802.

A modification of the second exemplary embodiment will be described. Theconfiguration of a wireless charging system and the configurations ofapparatuses in the wireless charging system are similar to those in thefirst exemplary embodiment, and therefore description thereof will beomitted. FIG. 9 is a flowchart illustrating a foreign substancedetection process performed by the power transmission apparatus 101 (theTX 101) according to the modification of the second exemplaryembodiment. The TX 101 according to this modification executesprocessing similar to the processing illustrated in FIG. 4, but executesprocessing illustrated in FIG. 9 in the foreign substance detection insteps F406 and F412. Description of a processing content similar to thatin FIG. 4 will be omitted.

In step F901, the TX 101 measures the Q factor. The method for measuringthe Q factor is similar to that in the first exemplary embodiment, andtherefore description thereof will be omitted. In step F902, the TX 101monitors whether a signal transmitted from the RX 102 is received beforethe time when a certain time elapses from the timing when the voltagevalue of the power transmission coil 205 is measured to calculate the Qfactor. The certain time at this time is the time assumed to be requiredfrom the start of the transmission of the signal from the RX 102 to theTX 101 to the completion of the transmission. If the RX 102 transmits asthe signal, for example, data packets including information indicatingpower received by the RX 102, a predetermined time is required from thestart of the transmission of the data packets to the completion of thetransmission. The period during which the TX 101 stops the applicationof power to the power transmission coil 205 to calculate the Q factormay be a period shorter than the time required for the RX 102 totransmit the data packets. Thus, if the TX 101 stops the application ofpower to the power transmission coil 205 and measures the voltage valuein the middle of the period when the RX 102 transmits the data packets,the remaining data packets are transmitted also after the timing whenthe voltage value is measured. The TX 101 can determine thatcommunication is performed based on the reception of a data packetbefore the time when the time assumed to be required for the RX 102 totransmit the data packets elapses from the clock time when theapplication of power is stopped.

If the TX 101 receives a signal such as a data packet before the timewhen the certain time elapses, the TX 101 determines that communicationwas performed (YES in step F903). Then, there is a possibility that themeasured voltage value is inappropriate for the calculation of the Qfactor for use in the foreign substance detection, and therefore, instep F901, the TX 101 measures the Q factor again. If the TX 101 doesnot receive a signal such as a data packet before the time when thecertain time elapses, the TX 101 determines that communication was notperformed (NO in step F903). Then, the TX 101 determines that themeasured voltage value is appropriate for the calculation of the Qfactor for use in the foreign substance detection. Then, in step F904,the TX 101 performs a determination process in the foreign substancedetection. The processes of steps F904 to F906 are similar to theprocesses of steps F803 to F805 in FIG. 8, and therefore descriptionthereof will be omitted.

As described above, the TX 101 according to this modification determineswhether communication was performed based on the reception of a signalwithin a certain time from the timing when the voltage value of thepower transmission coil 205 is measured to calculate the Q factor. TheTX 101 according to the second exemplary embodiment is configured todetermine whether communication is performed in the period during whichthe application of the voltage is stopped. However, the time duringwhich the application of the voltage is stopped is a period extremelyshort compared to the time required for the communication. Thus, todetect the communication status in the period during which theapplication of the voltage is stopped, the accuracy of the detectionneeds to be a certain level or more. According to this modification, itis only necessary to enable the detection of the communication status ina longer time, and thus, for example, it is possible to analyze thecommunication status using a processing program operating in the controlunit 201.

Although FIG. 9 illustrates an example of the processing in which themeasurement of the voltage value of the power transmission coil 205 andthe calculation of the Q factor based on the voltage value are performedin step F901, the calculation of the Q factor based on the voltage valuemay be performed after step F902.

If communication was performed at the timing when the voltage value ofthe power transmission coil 205 was measured to calculate the Q factor,the TX 101 according to each of the second exemplary embodiment and themodification of the second exemplary embodiment does not use the Qfactor based on this measured value in foreign substance detection.Embodiments of the present disclosure, however, are not limited to thisconfiguration. For example, by giving a lower priority to the Q factorbased on the voltage value measured in the period during whichcommunication is performed than the Q factor based on the voltage valuemeasured in the period during which communication is not performed, theTX 101 can use the Q factor based on the voltage value measured in theperiod during which communication is performed in other embodiments. Forexample, in a case where the Q factor is measured multiple times as inthe first exemplary embodiment, first, the TX 101 performs the processof determining whether a foreign substance is present based on the Qfactor based on the voltage value measured in the period during whichcommunication is not performed. Next, the TX 101 can confirm and correctthe result of the determination process using the measurement result ofthe Q factor based on the voltage value measured in the period duringwhich communication is performed. Alternatively, the TX 101 may estimatein advance the voltage value that changes by communication beingperformed, and based on the estimated value, correct the measurementresult of the Q factor based on the voltage value measured in the periodduring which communication is performed, and use the correctedmeasurement result, in some embodiments.

Other Exemplary Embodiments

The above-described foreign substance detection based on the measurementof the Q factor is performed every time the timeout time elapses.Embodiments of the present disclosure, however, are not limited to thisconfiguration. Alternatively, for example, a configuration may beemployed in which the foreign substance detection based on themeasurement of the Q factor is performed at the timing when a useroperation is performed on the TX 101 or the RX 102, in addition to everytime the timeout time elapses in other embodiments. In addition,alternatively, for example, the TX 101 may include a sensor fordetecting a vibration, the temperature, or the weight of an objectplaced in the power transmittable range, and when a vibration, a rise inthe temperature, or a change in the weight is detected, foreignsubstance detection may be executed, in some embodiments.

The parameters such as the reference value Qx, the threshold Th, thetimeout time, the number of measurement times, the certain number, thepredetermined time intervals, the number of successive times, thepredetermined time, and the certain time used in the above exemplaryembodiments are fixed values determined in advance. Embodiments of thepresent invention, however, are not limited to these features. Theseparameters may dynamically change according to the state of theapparatus, a change in the surrounding environment, or the executionstate of the processing, for example. For example, these parameters maybe determined by negotiation between the TX 101 and the RX 102 in thenegotiation phase.

The TX 101 according to each of the above exemplary embodiments measuresthe Q factor based on a change of the voltage inside the powertransmission coil 205 over time. Embodiments of the present disclosure,however, are not limited to this method. The TX 101 can also measure theQ factor based on a change of the current inside the power transmissioncoil 205 over time in other embodiments. In this case, the TX 101measures a current value A3 at the clock time T3 and a current value A4at the clock time T4, and using the measured current values A3 and A4and the frequency of a high-frequency current, calculates the Q factorbased on equation 1, for example.

Alternatively, the TX 101 may perform foreign substance detectionwithout calculating the Q factor. In FIG. 5B, for example, the TX 101measures voltage values A1 and A2 at the clock times T3 and T4 in theperiod during which the application of the voltage to the powertransmission coil 205 is stopped. Based on the difference (the slope)between the voltage values A1 and A2 in the period from the clock timeT3 to the clock time T4 based on the measurement results, the TX 101determines whether a foreign substance is present. It is assumed that ina case where a foreign substance is present in the power transmittablerange, the voltage value of the power transmission coil 205 attenuatesmore than in a case where a foreign substance is not present. Thus, ifthe difference (the slope) between the measured voltages is greater by acertain amount than a reference value acquired in a case where a foreignsubstance is not present (the difference between the voltages at twoclock times), the TX 101 determines that a foreign substance is present.Alternatively, the TX 101 can perform foreign substance detection alsoby obtaining the ratio between the voltage values A1 and A2. Forexample, if the ratio of the voltage A1 at the clock time T1 to thevoltage A2 at the clock time T2 is greater by a certain amount than areference value acquired in a case where a foreign substance is notpresent (the ratio between the voltages at two clock times), the TX 101determines that a foreign substance is present.

In a case where foreign substance detection is performed withoutcalculating the Q factor as described above, it is possible that thedifference and the ratio between the voltages to be calculated differaccording to the magnitude of the voltage applied to the powertransmission coil 205 or the timing when the voltage is measured. Thus,the magnitude of the voltage and the timing when the voltage is measuredare made the same as the conditions when the reference value isacquired, whereby it is possible to perform more secure foreignsubstance detection.

The TX 101 according to each of the above exemplary embodiments measuresone or both of a voltage and a current output from the powertransmission coil 205 and performs foreign substance detection based onthe measurement result. Embodiments of the present invention, however,are not limited to this configuration. For example, a configuration maybe employed in which another apparatus externally connected to the TX101 measures and calculates a voltage, a current, and power output fromthe power transmission coil 205, and energy accumulated in a capacitorin the TX 101 and provides the obtained values to the TX 101 in otherembodiments. The TX 101 can perform foreign substance detection based onthe values provided by another apparatus, for example.

The TX 101 according to each of the above exemplary embodiments isconfigured to, when the Q factor is measured, switch the switch in thepower transmission unit 203 and disconnect the connection with the powertransmission coil 205, thereby stopping the application of the voltageto the power transmission coil 205. Embodiments of the presentdisclosure, however, are not limited to this configuration.Alternatively, for example, when the Q factor is measured, the powertransmission unit 203 may set the power transmission voltage to 0,thereby stopping the application of the voltage, in other embodiments.In addition, alternatively, a configuration may be employed in whichwhen the Q factor is measured, the power transmission voltage is notcompletely set to 0, but is switched to a lower voltage value, forexample. However, in some embodiments, since the method for measuringthe Q factor according to the present exemplary embodiment calculatesthe Q factor based on the degree of the attenuation of the voltagevalue, the power transmission voltage is reduced to at least a voltagevalue that enables the observation of the attenuation of the voltagevalue, whereby it is possible to measure the Q factor without completelystopping the application of the voltage. At this time, if the periodduring which the voltage is reduced exceeds a certain time, there is apossibility that the RX 102 determines that an error has occurred in theTX 101. Thus, it is desirable to set the range of reduction in thevoltage value that enables the measurement of the attenuation of thevoltage in the period during which the RX 102 does not determine thatthe TX 101 is abnormal.

The TX 101 according to each of the above exemplary embodiments stopsthe voltage and measures the Q factor, thereby performing foreignsubstance detection. In each of the exemplary embodiments, however,there is a possibility that the RX 102 determines that an error hasoccurred in the TX 101 by stopping the voltage. Thus, a description isgiven of a method for solving the above issue by the RX 102 acquiringinformation regarding the TX 101 when the RX 102 is placed in the powertransmittable range of the TX 101.

For example, through communication in the negotiation phase, the RX 102transmits to the TX 101 a signal instructing the TX 101 to transmitinformation regarding the TX 101. The information regarding the TX 101includes version information regarding the TX 101, information regardinga standard w the TX 101 is compliant with, and information regarding aforeign substance detection method employed by the TX 101. The TX 101transmits the information regarding the TX 101 to the RX 102. Based onthe acquired information, the RX 102 recognizes that the TX 101 stopsthe voltage for a predetermined period to measure the Q factor.Consequently, in a case where the TX 101 stops the application of thevoltage to measure the Q factor, it is possible to prevent the RX 102from erroneously determining that an error has occurred in the TX 101,and stably continue a charging process.

According to the present disclosure, in a case where foreign substancedetection is performed based on the measurement result of a voltage or acurrent in the period during which the transmission of power is stopped,it is possible to prevent a decrease in the detection accuracy.

Other Embodiments

Embodiment(s) of the present disclosure can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the exemplary embodiments have been described, it is to beunderstood that the invention is not limited to the disclosed exemplaryembodiments. The scope of the following claims is to be accorded thebroadest interpretation so as to encompass all such modifications andequivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2020-022902, filed Feb. 13, 2020, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A power transmission apparatus comprising: acommunication unit configured to wirelessly communicate with a powerreception apparatus using an antenna; a power transmission unitconfigured to wirelessly transmit power to the power reception apparatususing the antenna; a measurement unit configured to, in a period duringwhich the transmission of the power from the power transmission unit isstopped, measure one or both of a voltage and a current output from theantenna; a first determination unit configured to perform, based on ameasurement result obtained by the measurement performed by themeasurement unit, a determination process for determining that an objectdifferent from the power reception apparatus is present; a restrictionunit configured to, in a case where it is determined that an objectdifferent from the power reception apparatus is present as a result ofthe determination process performed by the first determination unit,restrict the transmission of the power from the power transmission unit;and a control unit configured to control the first determination unitnot to use in the determination process the measurement result obtainedby the measurement performed by the measurement unit in a period duringwhich communication is performed by the communication unit.
 2. The powertransmission apparatus according to claim 1, wherein, in a case wherethe measurement unit performs the measurement in the period during whichcommunication is performed by the communication unit, the control unitcontrols the measurement unit to perform the measurement again.
 3. Thepower transmission apparatus according to claim 2, further comprising asecond determination unit configured to determine whether communicationis performed by the communication unit at a timing when the measurementis performed by the measurement unit, wherein, in a case where thesecond determination unit determines that communication is performed bythe communication unit at the timing when the measurement is performedby the measurement unit, the control unit controls the measurement unitto perform the measurement again.
 4. The power transmission apparatusaccording to claim 3, wherein, in a case where communication isperformed by the communication unit in the period during which thetransmission of the power from the power transmission unit is stopped,the second determination unit determines that communication is performedby the communication unit at the timing when the measurement isperformed by the measurement unit.
 5. The power transmission apparatusaccording to claim 3, wherein, in a case where communication isperformed by the communication unit in a period from a timing when themeasurement is performed by the measurement unit to a time when acertain time elapses, the second determination unit determines thatcommunication is performed by the communication unit at the timing whenthe measurement is performed by the measurement unit.
 6. The powertransmission apparatus according to claim 5, wherein the certain time isa time based on a time required from when the communication unit startsreception of a signal transmitted from the power reception apparatus towhen the communication unit ends the reception of the signal.
 7. Thepower transmission apparatus according to claim 1, wherein themeasurement unit measures the voltage output from the antenna at a firsttiming in the period during which the transmission of the power from thepower transmission unit is stopped and a second timing after the firsttiming in the period during which the transmission of the power from thepower transmission unit is stopped, and wherein the first determinationunit determines, based on the first timing, the second timing, ameasured value of the voltage output from the antenna based on the firsttiming, and a measured value of the voltage output from the antennabased on the second timing, that an object different from the powerreception apparatus is present.
 8. The power transmission apparatusaccording to claim 1, wherein the measurement unit measures the currentoutput from the antenna at a first timing in the period during which thetransmission of the power from the power transmission unit is stoppedand a second timing after the first timing in the period during whichthe transmission of the power from the power transmission unit isstopped, and wherein the first determination unit determines, based onthe first timing, the second timing, a measured value of the currentoutput from the antenna based on the first timing, and a measured valueof the current output from the antenna based on the second timing, thatan object different from the power reception apparatus is present. 9.The power transmission apparatus according to claim 7, wherein the firstdetermination unit determines, based on a length of time from the firsttiming to the second timing and a ratio of the measured value based onthe first timing to the measured value based on the second timing, thatan object different from the power reception apparatus is present. 10.The power transmission apparatus according to claim 9, wherein, in acase where a quality factor calculated based on the length of time fromthe first timing to the second timing and the ratio of the measuredvalue based on the first timing to the measured value based on thesecond timing is smaller than a predetermined reference, the firstdetermination unit determines that an object different from the powerreception apparatus is present.
 11. The power transmission apparatusaccording to claim 10, wherein the predetermined reference isinformation based on a result of the measurement performed by themeasurement unit in a state where an object different from the powerreception apparatus is not present.
 12. The power transmission apparatusaccording to claim 7, wherein, in a case where a difference between themeasured value based on the first timing and the measured value based onthe second timing is greater than a predetermined reference, the firstdetermination unit determines that an object different from the powerreception apparatus is present.
 13. The power transmission apparatusaccording to claim 1, wherein, in a case where it is determined that anobject different from the power reception apparatus is present, therestriction unit restricts the transmission of the power from the powertransmission unit so that the power transmitted from the powertransmission unit is smaller than in a case where it is not determinedthat an object different from the power reception apparatus is present.14. The power transmission apparatus according to claim 1, wherein in acase where it is determined that an object different from the powerreception apparatus is present, the restriction unit restricts the powertransmission unit from transmitting the power.
 15. The powertransmission apparatus according to claim 1, wherein the firstdetermination unit determines that an object different from the powerreception apparatus is present in an area where the power transmissionunit can transmit power to the power reception apparatus.
 16. A methodfor controlling a power transmission apparatus, the method comprising:wirelessly communicating with a power reception apparatus using anantenna; wirelessly transmitting power to the power reception apparatususing the antenna; measuring, in a period during which the transmissionof the power is stopped, one or both of a voltage and a current outputfrom the antenna; performing, based on a measurement result obtained bythe measurement, a determination process for determining that an objectdifferent from the power reception apparatus is present; restricting thetransmission of the power, in a case where it is determined that anobject different from the power reception apparatus is present in thedetermination process; and performing control not to use in thedetermination process the measurement result obtained by the measurementin a period during which communication is performed.
 17. Anon-transitory computer-readable storage medium storing a program forcausing a computer to execute a method, the method comprising:wirelessly communicating with a power reception apparatus using anantenna; wirelessly transmitting power to the power reception apparatususing the antenna; measuring, in a period during which the transmissionof the power is stopped, one or both of a voltage and a current outputfrom the antenna; performing, based on a measurement result obtained bythe measurement, a determination process for determining that an objectdifferent from the power reception apparatus is present; restricting thetransmission of the power, in a case where it is determined that anobject different from the power reception apparatus is present in thedetermination process; and performing control not to use in thedetermination process the measurement result obtained by the measurementin a period during which communication is performed.